Test your SMTP server connection, verify your SPF, DKIM, DMARC, and PTR records, check your IP against major blacklists, and get a full spam score analysis — all in one place, completely free. No software to download, no sign-up required.
SMTP Tester
Test your SMTP server and analyse your email infrastructure
What Does This SMTP Tester Check?
- SMTP connection — verifies that your mail server is reachable and accepting connections on your chosen port
- SPF record — checks whether your sending domain has a valid Sender Policy Framework record in place
- DKIM signature — verifies your DomainKeys Identified Mail configuration to confirm emails are signed correctly
- DMARC policy — checks your Domain-based Message Authentication, Reporting and Conformance record
- MX records — inspects your mail exchange records to confirm they are correctly configured
- PTR record — checks that your sending IP has a valid reverse DNS record
- IP blacklist check — scans your sending IP against major email blacklists to identify deliverability issues
- Spam score — analyses your email setup and gives an overall score to help you identify areas for improvement
How to Test Your SMTP Server
- Enter your SMTP connection details — add your SMTP server address, port, encryption type, username, and password. Your password is used only during the test and is never stored.
- Choose your test type — run a basic connection test to verify your server is reachable, or run a detailed analysis to check your full email infrastructure including SPF, DKIM, DMARC, blacklists, and spam score.
- Enter a recipient address for the detailed test — send the test email to yourself to verify full end-to-end delivery.
- Review your results — get a clear breakdown of every check, with actionable guidance on anything that needs attention.
What Is SMTP?
SMTP stands for Simple Mail Transfer Protocol. It is the standard protocol used to send emails across the internet. When you send an email — whether from Gmail, Outlook, or your own mail server — SMTP is the protocol that handles the transmission. Understanding how your SMTP server is configured is essential for ensuring your emails reach the inbox reliably and do not get flagged as spam.
Common SMTP Ports
| Port | Encryption | Use case |
|---|---|---|
| 587 | TLS(STARTTLS) | Standard submission port — recommended for most setups |
| 465 | SSL | Legacy SSL port — still widely supported |
| 25 | None | Server-to-server delivery — often blocked by ISPs for outbound mail |
| 2525 | TLS | Alternative port used when 587 is blocked |
Why Email Deliverability Testing Matters
Even if your SMTP server is technically working, your emails can still fail to reach the inbox. Misconfigured SPF, DKIM, or DMARC records — or a sending IP that appears on a blacklist — are among the most common reasons legitimate emails are filtered as spam or rejected outright.
Regular testing is especially important after changing your mail server, switching email providers, or setting up a new domain. A single misconfiguration can silently affect your deliverability for days or weeks before you notice.
Nesdzo’s SMTP Tester gives you a complete picture of your email infrastructure in one test — so you can identify and fix issues before they affect your communication.
Do I Need to Download Software to Test My SMTP Server?
No. Nesdzo’s SMTP Tester runs entirely online — there is nothing to download or install. Open the tool in your browser, enter your server details, and run the test immediately. It works on any device with a modern browser, including Windows, Mac, Linux, and mobile.
Frequently Asked Questions
What does SMTP stand for? SMTP stands for Simple Mail Transfer Protocol. It is the standard protocol used to send emails between mail servers and from email clients to mail servers.
Is my password stored when I run the test? No. Your SMTP password is used only to authenticate the test connection and is never stored, logged, or transmitted beyond the test itself.
What SMTP port should I use? Port 587 with TLS is the recommended port for most outbound email setups. Port 465 with SSL is also widely supported. Port 25 is used for server-to-server delivery but is often blocked by ISPs for outbound mail.
What is an IP blacklist? An IP blacklist is a database of IP addresses known or suspected to send spam. If your sending IP appears on a blacklist, receiving mail servers may reject or filter your emails. Nesdzo’s SMTP Tester checks your IP against major blacklists and reports the results.
What is a spam score? A spam score is a rating that reflects how likely your emails are to be filtered as spam. It is calculated based on factors including your SPF, DKIM, and DMARC configuration, your IP reputation, and the content of your test email.
What is the difference between SPF, DKIM, and DMARC? SPF verifies which IP addresses are authorised to send email on behalf of your domain. DKIM adds a cryptographic signature to your emails to confirm they have not been tampered with in transit. DMARC ties both together and tells receiving servers what to do when an email fails authentication. All three work together to protect your domain and improve deliverability.
Is this SMTP tester free? Yes. Nesdzo’s SMTP Tester is completely free with no limits and no sign-up required.